Process for the digestion of vegetable growths to produce cellulose



Patented Jan. 8, 1935 I a 1,987,195

UNITED STATES PATENT OFFICE PRbCESS FOR THE DIGESTION OF VEGE- iljglgLEGROWTHS TO PRODUCE CELLU- Herman B. Kipper, Accord, Mass.

No Drawing. Application March 3, 1934,

SerialNo. 713,856

6 Claims, (01. 92-9) In my Patent Number 1,820,276 'of August 25, abovedigester was partially filled with some 1931 I described processing fordigestion of vegtwenty pounds of waste cotton seed hulls and a etablegrowths and more especially wood for hot aqueous solution containingfrom five to production of cellulose and more especially paper fifteenpercent of sodium hydroxide on the 6' pulp. According to the processingdescribed in weight of waste hulls was run into the same until '5 theabove patent mechanical disintegration of about three-fourths filled.The heater blades the wood is established simultaneously with travelingat about a speed of twenty feet per secchemical disintegration ordigestion by means of nd and nine hundred revolutions per minutebevelled bars or knives which travel with cylinwere then started andoxygen forced into the 10 drical motion within the digester and throughbottom of the digester at a rate of about ten cubic 10 the digestionmass at a high rate of speed. Refeet per hour. Digestion was continuedfor seven ductions in the chemicals required and in the u s. e pulp Wasthen removed, the digestime and temperature of digestion are therebyestion liquor drawn off from the pulp by means of tablished. In mycopending applications Serial a suction filter and the pulp suitablywashed. A

' Nos. 660,649 of March 14, 1933, 665,957 of April good pulp high inalpha-cellulose was secured. 15

13, 1933, 682,942 of July '31, 1933 and 689,875 of The spent digestionliquor, of course, can be evap- September 18, 1933, I describe specificimproveorated for recovery of chemicals or again it may ments indigestion media as applied to my basic be evaporated t dry A plasticmaterial is method of processing. v secured by the latter step which isadaptable for My present invention embodies a further immouldingpurposes. 20

provement over the above processing for diges- I have also employedoxygen at a superatmostion of vegetable growths for recovery of cellu- Do p su e a d p to fifty p d and at lose. Such improvement depends moreespecially e y-five to O hundred d g Centigrade on a further reductionin the temperature redigestions otherwise similar to that justdescribed.

quired for digestion and hence positive further h di sti p ri d is th ymat ia ly r 25 reduction in the fuel requirement. In order to duced. Thesame was comp Within about an accomplish this latter result air oroxygen is eu I @1 50 used a r in Place Of Oxygen in a passed into thedigester and through the digestion estion practically t Same a thosealready, liquid or mass. Such air or oxygen may be passed scribed withthe exception that about five times into the digester at the bottom ofthe same, or the V e o a w s d instead of the Oxygen 30 through aperforated hollow shaft bearing the as a ady noted a the pressure wasmaindisintegration bars or knives, or again in any ned at about ohundred p d The Oxygen other suitable manner, as at the ends of my horiar g t, of-e be circulated through the zontal digester. I have usedsatisfactorily all digester y a p p Situated externallythree methodsmentioned. When employing this Furtherm r f t d s i n agents I have 35method of digestion I have found it necessary to ed Ca c u hydroxide,ten to fifteen Percent employ only a hot aqueous solution of the dion"the weight of hulls suspended in the digestion gestion chemicals and airor oxygen at atmosmass, and calcium hydroxide in conjunction with phericor superatmospheric pressure. In other sodium chloride, from one to fiveper in .0 words, the digestion solution need not be heated so ut on.Calciu hydroxide 18 Of Course, Only 40 above its boiling point. Thismethod of digesvery slightly soluble. Equilibrium between the tion Ihave found especially advantageous for sodium chloride and calciumhydroxide in soluuse'in the recovery of the cellulose fibre from tionoccurs and a small percentage of sodium waste cotton seed hulls.hydroxide is formed. As the latter is quickly In digestion of thesewaste hulls from their utilized in the digestion process itsregeneration 45 cellulose content I'used a small digester two feet withestablishment of equilibrium is brought long by sixteen inches internaldiameter. A about, so that a small percentage of sodium hyquarter inchpipe coil was wound externally droxide is constantly available for thedigestion. around the digester and used for heating the The latter isfar more active than the correlatter with steam. For large scaleoperation such sponding calcium hydroxide, but so-called hy- 50 externalheating should be practically unnecesdrated lime is, of course, much thecheaper chemsary as the ratio of -surface'to cubical contents ical sothat its use is greatly tobe preferred. in the latter case would begreatly reduced and Without the rapid mechanical mixing or disin- 6hence surface radiation of heat correspondingly tegrationemployed in mytype of digester the'use lessened. Insulation might be required. llhe ofsuch lime, however, is impracticable-and such statement furthermore isvery nearly pertinent to the use of oxygen or air for the digestionsdescribed. As the percentage of sodium hydroxide present in the solutionat any given time, however, is small, the digestion period isconsiderably increased and six to eight hours were required.

- In order to establish the more rapid digestion of nitrogen, or nitricacid vapor, or soaked in an aqueous solution of ten to twenty percentnitric acid. Subsequent to such treatment, however,

' I have found that I could use hydrated'lime or calcium hydroxide forfibre production also in conjunction with oxygen or air, in place ofsodium hydroxide for final fibre liberation. The latter step is of greatadvantage because of the reduced cost of the calcium hydroxide, orhydrated lime, in comparison with that of the similar sodium salt.

The wood chips were first steamed to about a twenty percent moisturecontent andthen treated for two to three hours with air at about fifteenpounds super-atmospheric pressure andwith five to fifteen percent of theoxide of nitrogen and under constant mechanical beating as induced in mypatented type of digester. The air supply was renewed continuously sothat about ten to twenty percent of oxygen on the weight of wood wasemployed. Hot water containing ten to twenty percent, on the weight ofwood, of calcium hydroxide in suspension was then run into the digesterand beating continued for from one to two hours also undersuper-atmospheric pressure produced by air. In the latter case I usedabout fifty pounds pressure. It will be understood that the rapidlymoving digestion mass is mechanically sprayed through the compressed airsituated above it and hence forced penetration of the mass by oxygencontinuously established. It

.' steamed into the digester. I Otherwise the processing was practicallythat described.

When pretreating the wood with nitric acid about fifteen to twentypercent of the latter diluted with water was used, and the wood allowedto soak for some twenty-four to forty-eight hours depending on the sizeof the wood chips. It was then treated with air at about fifteen poundssuperatmospheric pressure in my type of digester for an hour or two atfifty to one hundred degrees centigrade. The processing subsequentlyused was that already described. In the soaking process the percentageof nitric acid required is about double that needed in the first twomentioned methods so that the latter process is not relatively asefllcient. I have used also a calcined dolomite stone in place oflimestone, or a hydrate secured from the former.

The pulpin such case is somewhat lighter in color. I have further usedsodium hydroxide in conjunction with calcium and magnesium hydroxide. Y

A limitless number of combinations of different chemicals in alkalinedigestion'liquors, in place of those described, might of course beemployed. I used'sodium nitrate and nitrite as well as sodium sulphite,and a combination of sodium nitrate and sodium sulphite in thisconnection,

but without any very distinct advantages. Also other oxidizing agents aspotassium permanganate andpotassium dichromate were not found ofsufficient added advantage to warrant the additional costs involved intheir use. I have used only hot aqueous solutions of the digestionchemicals, as such were found entirely satisfactory, but, of course,higher temperatures and superatmospheric steam pressures might beemployed with consequent reduction in thedigestion periods. On the otherhand if colder digestion liquors are used we should expect to have toemploy longer digestion periods. Although I have not used cold liquors Ihave employed the same heated only to fifty degrees centigrade and foundsuch use as positive.

. In freeing the cellulose from cotton seed hulls I have also usedhydrated lime, or calcium hydroxide, in place of sodium hydroxide, ormixtures of these two chemicals, in conjunction with oxygen or air. Forthe latter step I employed about eighty per cent of lime, or the fullequivalent of lime required and twenty per cent of sodium carbonate.Again I have brought about the digestion with sodium hydroxide, andafter separation of the cellulose fibre from the spent hot digestionliquor I have treated the latter under stirring. The partially oxidizedhull material is thereby precipitated as the calcium salt and the sodiumhydroxide solution is regenerated for digestion purposes. The calciumsalt of the oxidized hull material after drying, and while hot,isplastic and under pressure can be molded.

I have also used sodium andcalcium hydroxides for wood digestion, butwithout oxygen, but

even in my type of digester seventy five to one hundred pounds steam Iclaim: v 1. In a process for the digestion of vegetable growths toproduce cellulose fibre and of disintegrating the said vegetablematerial mechanically by the action of cylindrically rapidly movingpressure are required.

metal pieces which travel through the digestion mass simultaneously withthe process of digestion by chemicals in aqueous solution the step offorcing oxygen (air) through the digestion mass simultaneously to theperiod of chemical digestion.

2. In a process for the digestion of vegetable growths to producecellulose fibre and of disintegrating the said vegetable materialmechanically by the action of cylindrically rapidly moving metal pieceswhich travel through the digestion mass simultaneously with the processof digestion by chemicals in aqueous solution the step of forcing oxygen(air) at superatmospheric pressure through the digestion masssimultaneously to the sure through the digestion mass simultaneously tothe period of chemical digestion.

4. In a process for the digestion of vegetable growths to producecellulose fibre. and of disintegrating the said vegetable materialmechanically by the action of cylindrieally rapidly moving metal barswhich travel through the digestion mass simultaneously to the saiddigestion process the step of digesting the vegetable matter by a hotaqueous solution of sodium hydroxide produced from sodium carbonate inthesaid solution and of calcium hydroxide suspended in the digestionmass and the step of forcing oxygen (air) at superatmosphericpressurethrough the digestion mass simultaneously to the period ofchemical digestion.

5. In a process for the digestion of vegetable growths to producecellulose fibre and of disin-' tegrating the said vegetable materialmechanically by the action of cylindrically rapidly moving metal barswhich travel through the digestion mass simultaneously to the saiddigestion process the step of pretreating the vegetable matter withsteam, oiwgen, (air) and nitric oxides (nitric acid) and the step ofdigesting the said matter with calcium hydroxide suspended in hot waterand added to the digestion mass and finally the step of'forcing oxygen(air) through the digestion mass simultaneously to theperiod. ofchemical digestion and by-means oi the rapidly traveling beater elementsand with or without exterior circulation of the gas.

6. In a process for the digestion of vegetable growths to producecellulose fibre and of disintegrating the said vegetable materialmechanically by the action of cylindrically rapidly moving metal barswhich travel through the digestion mass simultaneously to the saiddigestion process the step of pre-treating wood chips with steam, oxygen(air) and nitric oxides (nitric acid) at superatmospheric pressure andthe step of digesting the said treated wood chips with calcium hydroxidesuspended in hot water and added to the digestion mass and finally thestep of forcing oxygen (air) at superatmospheric pressure through thedigestion mass simultaneously to the period of chemical digestion and bymeans of the rapidly traveling beater elements and with or withoutexterior circulation.

HERMAN B. KIPPER.

